Composition for sealing porous formations in oil and gas wells



Patented June 10, 1952 comosrrloxron SEALING POROUS-FOR.- -;MATIONSJN IL AND GAS WELLS 1 hiijiibell; Corpus" Christi, and 'H iiiei" L'MingSanAntonio, Tex.; 9 to sa d-T said Campbell Nam-swing. "Application Jiine 23, 1949, i N0. 100,972

The invention relates the "are er drillin wells and has reference in particular animproved andsatisfactory"fluid'iniirture for preventing the partialbroorhplt' nest-r circulation during rotary 'b serationsoime loss of the drilling fluid when drilling with cable In the drilling of awellf forfei'i'ainple', to {obtain petroleum oil, a fluid or 'iniid i's 'ex'riployed which may comprisea mixture 'ofw'aterjgelforming material such "as an bntoriite afnd'the like, weighting materials arid special additives 'for plugging or sealing "the wins of 'thewelllbo're to prevent loss of thefiuidto the suiroundingr rmations. The'primarffunctioh 'of the drilling fluid is to lubricate and coofthe drilling tool and to suspend the cuttings ncur the Hrillingoperation so that they are cairried'to the surfaceeither by bailing the well boreasin'cable 'tool' drilling or by circulation of the 'fluidinrotary "drilling, In said rotary drilling operations the-fluid flows through the drilling pipe into thewellboi'e under pressure and returns to the-surface-"in th'espace between the pipe and sidewalls of'thebore, and accordingly other functions of *the drilling fluid are tokeep dawn-re ara ion; pressures by the weight of the -fli'fldand tol'seal the walls of the bore to'prev'ent 'o'r'miniinizeloss of the drilling fluid to the formations being penetrated. i

The problem'of lost circulation one or the most difficult of the many problem'seneountered in oil well drilling 'by the rotaryi'nethod.; As the drilling fluid is circulatedfinthe bore hole under a pressure exceeding that or the formation, the solid particles suspended"inithfluid'and also the colloidal ingredients of theflui d now'inm the formation throughthe interstices: passages and pores of the formation matfiaIJffLoSs of circulation, however, not encountered unless and in other patents Claims, (01; 2524.5)

relatingj'to "drilling" fluids the following materials are describedas efleetive'additives f or' iniproving theformationsealing properties of ordinary drilling 'muds: glue, easein,' milk. powder, blood albumin, "gelatin; gum, arabic, 1 copal seaweed, agar agarfcottons'eed hulls, linseedfcake, wheat flour,'corn starch, quebracho, p'y'sllium seed, dextrose, mo'ntan' wax,'"mica and asbestos fibers. Howeven'when highly permeable zones such as gravel pits and crevices are penetrated such materials fail'to bridge since as in the case of 'clay particles they are too small and they lack the necessaryjqualities'to eflect a blocking orstoppage of "thejflow; 'Of course, there are factors limiting the size of the particles 01 the solid additives, since as ingredients of'the drilling fluid they must be able to pass through the pump and they mustnotblog or otherwise interfere with pumping'operatlons. 4 r

Accordingly, an object of theinvention' is to provide materials for use as additives to: drilling fluids which will have such coaction in" combination witheac'h other as to eflectively seal porous fo'rmajtionsby the building of a strong but thin impervious] sheath. I i

Another object of the invention is to provide ingredients'for'drilling fluid which will meet the requirements'of an all-purpose additive to prevent loss of thefluid to surrounding formations. Another object of the invention is to provide drilling fluid additives for sealing the well bore and'which 'willnot interfere with the pumping of the drilling fluid, which will'not deteriorate substantially during the'drilling operation, and which will not readily separate out of the drilling fluid.

Another object 'is to prevent lost circulation by adding to thedrilling fluid materials such as 'wool'shoddy or cotton linters toiorxn a fibrous ceeds the rupture strength ofrtheflberst Hence,

the first considerationwasto selecta fiber 01' fibers having adequate strength with the required flexibility. Whereas, the strength of the fibers determines the limiting pressure applicable to any admixture, a measure of the flexibility or pliability of a fibrous substance is indicated by the filter cake thickness. This is due to the fact that the flexible fibers conform to the cavities in the formations, thereby plugging them and stopping further flow of mud. At least fibers that are flexible tend to conform, whereas stiff and inflexible fibers do not. Thus animal, vegetable or synthetic fiber will accomplish ths purpose of the present invention provided it has the required flexibility, fineness and textile strength. Length of the fiber is however important due to mechanical injections by means of pumps into the well bore and accordingly fibers longer than 4 inches are objectionable and fibers shorter than 4 inch fail to bridge except in sands of nylon and rayon. We prefer wool shoddy and cotton linters because these materials are cheap and generally available. For the filler component mentioned can be made of sawdust, ground corn cobs, and rice hulls. Such materials are relatively indestructible in the fluid and as regards the sawdust and ground corn cobs they can be secured in particle sizes covering a wide range.

Wool shoddy may consist of a mixture of wool fibers and jute fibers. At least this is true of /4 inch shoddy as purchased on the market at the present time. An analysis of 1 inch shoddy, known to be almost pure wool, indicated the nitrogen content of the same to be approximately 8.97 per cent, whereas, the one-quarter inch shoddy had a nitrogen content of approximately 4.35 per cent. Jute fibers do not contain more than a trace of nitrogen. Cotton linters are generally defined as the residual fibers removed from cottonseed by mechanical processes and said linters have been classified as mill run, first cut and second cu Any of these fibers will serve the purpose of the invention, provided they fulfill the main basic requirements for the fibrous material as herein noted. Staple cotton can also be used but as in the case with regular wool, nylon and also rayon, the cost is the controlling factor.

Since porous formations are usually of varying size a filler type plugging agent suitable for all formations should be one of variable size and accordingly the sawdust and ground corn cobs when used as a filler should comprise assorted size particles varying from 0.006 to 0.187 inch in diameter. Filler particles of smaller diameter than 0.006 is not necessary since the clay particles function for this range. Rice hulls will generally be used in combination with the sawdust or ground corn cobs.

Referring' more particularly to the filling material, considered as suitable for the present invention, the particle size distribution of the same is given in the following table:

Per cent Retained on No. 4 screen 0.0 Passing No. 4 but retained on No. 8 5.0 Passing No. 8 but retained on No. 16 10.0 Passing No. 16 but retained on No. 40.0 Passing No. 30 but retained on No. 50 30.0 Passing No. 50 15.0

The above table represents a preferred grading of the various size filler particles for an allpurpose additive, and the same is not intended to be restrictive or limiting, since the actual per- 4 centage for each screen size is not so critical as the mere presence of a substantial amount of each particle size. The number of openings per square inch determines the screen number. For example, a No. 4 screen contains four openings within the inch, and each opening is one-fourth inch square less the diameter of the wire used. A No. 8 screen contains eight openings within the inch providing openings which are one-eighth inch square, etc.

The effectiveness of the present ingredients as sealingcompounds has been adequately proven by actual tests and also by laboratory tests using specially designed equipment to simulate subsurface lost circulation conditions and wherein the present ingredients were combined with other materials, and were combined with sawdust particles of different size in order to determine the relationship between average pore size and average particle size for the best results. Two measurements were recorded, the maximum pressure required to force the mud through a gravel bed and. the thickness of the retaining mat on the latter. Obviously, the effectiveness of a plugging agent is denoted not only by the pressure required to rupture the fibers but by the thickness of the mat formed. The other materials included shredded cellophane, shredded bagasse, coarse flake mica, shredded redwood bark, balsam wood wool and mineral wool.

The addition of wool shoddy or cotton linters and sawdust to fluid admixtures including one or more of the said other 'materials had the effect of materially increasing the pressure before failure occurred and these additives also produced the minimum filter cake thickness. In some tests on a, certain character of gravel bed the use of wool shoddy and sawdust prov duced the best results and in other tests on dif- .made herein relating to the strength of the fibrous mat. In this test cotton, wool and lechuguilla fibers were employed. The latter is one of the vegetable fibers contemplated by the invention and is obtained from the lechuguilla cactus from which sisal rope is manufactured.

The particular eife'ctivness of the filler is somewhat related to the average pore size of the permeable formation. In cavernous type formations long fibers are required such as the one inch wool shoddy because of the larger size pores encountered, and for similar reasons it is desired to use graded sawdust or ground corn cobs having a high percentage of larger size particles. For general use the shorter length fibers are preferred as a more economical and better product is produced from the standpoint of mixing and pumping at the well. Also as-the average size of the pores decreases the sawdust can be graded in like manner with a decrease inthe larger sawdust particles in favor of the intermediate sizes. Of course it is not necessary to use fibers of the same length and the invention additionally contemplates a fluid admixture wherein the fibers are graded from approximately inch in length to 1 inch in length or thereabouts and with a filler 5, fibrous material and filler can be mixed in equal quantities. However, we have obtained satisfactory results in plugging a limestone formation with a composition containing equal parts by weight of sawdust, rice hulls and one fourth inch wool shoddy. With the rice hulls eliminated the drilling fluid composition of the invention may consist of equal parts by weight of sawdust and wool shoddy.

An important feature of the invention resides in the coaction of the sawdust particles with the fibrous mat produced by the fibers in bridging the pores or voids in the loose formations. The penetration of the plugging materials into the pores is entirely adequate for retention purposes and the impervious sheath which is quickly formed is characterized by maximum strength with minimum thickness.

What is claimed is:

1. A composition for sealing permeable formations encountered in the drilling of a well, comprising fibrous material and a filler in admixture therewith, said fibrous material comprising strong, fiexible fibers selected from the group consisting of jute, fiax, mohair, lechuguilla fibers, synthetic fibers, cotton, cotton linters, wool and wool shoddy, said fibrous material being present in proportions by weight from approximately 33% to 90% and including fibers of difierent lengths ranging from approximately one-fourth to four inches, and said filler being present in amounts up to 67% and comprising sawdust particles ranging in size but not smaller than .006 inch in diameter.

2. A composition for sealing permeable i'orma tions encountered in the drilling of a well, comprising fibrous material and a granular filler in admixture therewith, said fibrous material comprising strong, fiexible fibers selected from the group consisting of jute, fiax, mohair, lechuguilla fibers, synthetic fibers, cotton, cotton linters, wool and wool shoddy, said fibrous ma terial being present in proportions by weight from approximately 33% to 90% and including fibers of different lengths ranging from approximately one-fourth to four inches, and said granular filler being present in amounts up to 67% and comprising sawdust graded as to particle size so that not less than nor more than 40% will be retained on any screen of the following U. 8. series 8, 16, 30 and 50 and wherein all of the granular filler will pass a No. 4 screen.

3. A composition for sealing permeable formations encountered in the drilling of a well, comprising fibrous material and a granular filler in admixture therewith, said fibrous material comprising strong, fiexible fibers selected from the group consisting of jute, fiax, mohair, lechuguilla fibers, synthetic fibers, cotton, cotton linters, wool and wool shoddy, said fibrous material being present in proportions by weight from approximately 33% to 90% and including fibers of different lengths ranging from approximately onetourth to four inches, and said granular filler consisting of particles ranging in size but not substantially smaller than .006 inch in diameter, said filler being present in amounts up to 67% and being selected from the group consisting of ground corn cobs and sawdust.

4. A composition for sealing permeable formations encountered in the drilling of a well comprising fibrous material and a granular filler in admixture therewith, said fibrous material comprising strong, fiexible fibers selected from the group consisting of jute, fiax, mohair, lechuguilla fibers, synthetic fibers, cotton, cotton linters, wool and wool shoddy, said fibrous material being present in proportions by weight from approximately 33% to and including fibers of different lengths ranging from approximately oneiourth to four inches, said filler being selected from the group consisting of ground corn cobs and sawdust, said filler being present in amounts approximately 67% and being graded as to particle size substantially as follows:

Per cent Retained on No. 4 screen 0.0 Passing No. 4 but retained on No. 8 5.0 Passing No. 8 but retained on No. 16 10.0 Passing No. 16 but retained on No. 30 40.0 Passing No. 30 but retained on No. 50 30.0 Passing No. 50 15.0

5. In the drilling of a well, the method of preventing loss of the drilling fiuid to porous formations, which consists in incorporating in the drilling fiuid a sealing composition consisting of a mixture of fibrous material and a granular filler, said fibrous material comprising strong, flexible fibers selected from the group consisting of jute, fiax, mohair, lechuguilla fibers, synthetic fibers, cotton, cotton linters, wool and wool shoddy, said fibrous material being present in the mixture in proportions by weight from approximately 33% to 90% and including fibers of different lengths, said granular filler being present in the mixture in amounts up to 67% and being selected from the group consisting of ground corn cobs and sawdust with particles thereof graded as to size so that not less than about 5% nor more than 40% will be retained on any screen of the following U. S. series 8, 16, 30 and 50, with all of the granular filler passing a No. 4 screen, and pumping the drilling fluid with the sealing composition admixed therewith into the well bore, whereby to seal the porous formations to prevent the loss of drilling fiuid therethrough by the interweaving action of the fibers which produce a mat and by the action or the filler therewith which forms an impervious sheath in the formations.

JOHN G. CAMPBELL. HOMER L. TWINING.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,807,082 Boynton May 26, 1931 2,041,086 OBrien May 19, 1936 2,064,936 McQuiston Dec. 22, 1936 2,119,829 Parsons June 7, 1938 2,214,366 Freeland et al Sept. 10, 1940 2,398,347 Anderson Apr. 16, 1946 OTHER REFERENCES Sawdon, Lost Circulation in Rotary Holes, article in the Petroleum Engineer, Feb. 1936, pgs. 27 to 30.

Langton, Fibrous Materials Aid Restoring Lost Drilling Well Circulation, article in The Oil and Gas Journal, Apr. 23, 1936, pgs, 31, 33 and 34. 

1. A COMPOSITION FOR SEALING PERMEABLE FORMATIONS ENCOUNTERED IN THE DRILLING OF A WELL, COMPRISING FIBROUS MATERIAL AND A FILLER IN ADMIXTURE THEREWITH, SAID FIBROUS MATERIAL COMPRISING STRONG, FLEXIBLE FIBERS SELECTED FROM THE GROUP CONSISTING OF JUTE, FLAX, MOHAIR, LECHUGUILLA FIBERS, SYNTHETIC FIBERS, COTTON, COTTON LINTERS, WOOL AND WOOL SHODDY, SAID FIBROUS MATERIAL BEING PRESENT IN PROPORTIONS BY WEIGHT FROM APPROXIMATELY 33% TO 90% AND INCLUDING FIBERS OF DIFFERENT LENGTHS RANGING FROM APPROXIMATELY ONE-FOURTH TO FOUR INCHES, AND SAID FILLER BEING PRESENT IN AMOUNTS UP TO 67% AND COMPRISING SAWDUST PARTICELS RANGING IN SIZE BUT NOT SMALLER THAN 006 INCH IN DIAMETER. 